This invention relates to siloxane, silsesquioxane and modified silsesquioxane polymers.
Silicon dioxide (SiO2) thin films are an essential component of microelectronic devices and substrates that are currently in widespread usage. These SiO2-containing thin films are generally created using well-known silanes, e.g., H4Si, silane esters, e.g., tetraethoxysilane (TEOS), or silsesquioxanes, e.g., hydrogen silsesquioxane resins such as described in U.S. Pat. No. 5,290,354 of Haluska and U.S. Pat. No. 5,320,863 of Ballance et al.
Component (e.g., transistor) densities on microelectronic devices have continually increased in recent years, and the current development of ultra large scale integration (ULSI) technology, to implement in excess of 300,000 transistors per chip, places severe constraints on layered SiO2-containing thin films and coating application processes employed. The ULSI requirements for multilevel and submicron interconnections demand defect-free uniform silicon dioxide thin films that are not easily achieved with current coating application methodologies, such as spin-on glass (SOG) and chemical vapor deposition (CVD), using known SiO2-forming resins.
SOG ceramic thin films made from known SiO2-film forming materials typically exhibit voids if gap dimensions are less than 0.15 micron. Water evolution during curing of such SOG coating compositions results in high shrinkage and stressed films. SOG coating compositions using methyltriethoxysilane, instead of the more commonly used tetraethoxysilane (TEOS), require a greater degree of cure before plastic flow characteristics of the resin are overcome, which may adversely affect planarization characteristics.
CVD ceramic thin films made using TEOS can provide submicron interconnections but do not provide satisfactory high gap-fill capacity and reliability, a requirement of ULSI multilevel interconnections. The tendency of TEOS/CVD ceramic thin films to absorb water can lead to decreased reliability from degradation of metal interconnections. CVD ceramic thin films that incorporate boron or phosphorus exhibit improved process parameters but at the cost of sacrificed dielectric properties. CVD thin films derived from known silsesquioxanes, instead of TEOS or other silanes, exhibit reduced dimensional stability, particularly upon thermal cycling required for interlayer application.
Sommer et al., xe2x80x9cOrganosilicon Compounds V. xcex2-Eliminations Involving Silicon,xe2x80x9d J. Amer. Chem. Soc., 68, pp. 1083-1085 (1946) summarizes chemical reaction studies of xcex2-chloroethyltrichlorosilane and xcex2-chloro-n-propyltrichlorosilane, including synthesis of xcex2-chloroethyl silicone. The xcex2-chloroethyl silicone polymer, having a formula ClCH2CH2SiO1.5, was reacted with dilute alkali to give ethylene and Si(OH)4. No end use applications for these compounds were suggested.
In accordance with the present invention, a silsesquioxane polymer, useful for preparing SiO2-rich films, is the polymeric reaction product that is obtained from the hydrolysis and condensation polymerization of an organosilane containing a xcex2-substituted alkyl group, the organosilane having the general formula RnSiX(4-n) where n is 1 or 2; X is a halogen selected from the group consisting of chlorine, bromine, fluorine, and iodine, or an alkoxy selected from the group consisting of methoxy, ethoxy and propoxy substituents; and R is an alkyl group having at least one but not more than two xcex2-substituents that are electronegative, and wherein the polymeric reaction product contains silanol groups. The xcex2-substituted alkyl group, R in the general formula, is preferably an ethyl group or propyl group having at least one but not more than two xcex2-substituents selected from the group consisting of chlorine, bromine, fluorine, iodine, hydroxy, methoxy, ethoxy, and acetoxy
The xcex2-substituted organosilsesquioxane polymer of this invention may also contain at least one but not more than two xcex1-substituents on the xcex2-substituted alkyl group, the xcex1-substituent on the xcex2-substituted alkyl group being selected from the group consisting of chlorine, bromine, fluorine, iodine, hydroxy, methoxy, ethoxy and acetoxy. The xcex1-substituent on such a silsesquioxane polymer is preferably the same as the xcex2-substituent on the alkyl group.
A preferred embodiment of this invention is a silsesquioxane polymer, useful for preparing SiO2-rich films, that is the polymeric reaction product obtained from the hydrolysis and condensation polymerization of an organosilane containing a xcex2-substituted ethyl group, the organosilane having the general formula RnSiX(4-n) where n is 1 (i.e., the general formula becomes RSiX3); X is a halogen selected from the group consisting of chlorine and bromine or an alkoxy selected from the group consisting of methoxy and ethoxy substituents; and R is a xcex2-substituted ethyl group where the xcex2-substituent is mono- or di-substituted and is selected from the group consisting of chlorine, bromine, fluorine, hydroxy, methoxy, and acetoxy, the non-halogen xcex2-substituents being particuarly preferred.
This silsesquioxane polymer may also contain at least one but not more than two xcex1-substituents on the xcex2-substituted ethyl group, the xcex1-substituent being selected from the group consisting of chlorine, bromine, fluorine, hydroxy, methoxy and acetoxy. The xcex1-substituent on such a silsesquioxane polymer is preferably the same as the xcex2-substituent on the ethyl group.
A preferred xcex2-substituted organosilsesquioxane polymer of this invention, useful for preparing SiO2-rich films, is the polymeric reaction product that is obtained from the hydrolysis and condensation polymerization of an organosilane containing a xcex2-substituted ethyl group, the organosilane being xcex2-chloroethyltrichlorosilane, ClCH2CH2SiCl3. More preferred are the non-halogen substitutents at the xcex2 position.
The xcex2-substituted organosilsesquioxane polymeric reaction products of this invention contain free silanol groups. Such silsesquioxane polymer compositions are preferably polymeric reaction products that contain at least about five up to about 75 silanol groups per 100 silicon atoms and more preferably that contain about 20 to about 50 silanol groups per 100 silicon atoms.
The silsesquioxane polymer of this invention is preferably a polymeric reaction product that is obtained from homopolymerization of the organosilane. In alternative embodiments, the xcex2-substituted organosilsesquioxane polymer may be a polymeric reaction product that is obtained from copolymerization of the organosilane with an alkoxysilane, e.g., a tetraalkoxysilane or organic substituted alkoxysilane. The alkoxysilane is preferably selected from the group consisting of tetraalkoxysilanes such as tetraethoxysilane (TEOS), tetramethoxysilane (TMOS), methoxytriethoxysilane, triethoxychlorosilane, and organic substituted alkoxysilanes such as bis(xcex2-chloroethyl)dichlorosilane, bis(trimethoxysilyl)ethane, methyltriethoxysilane, vinyltriethoxysilane, pentafluorophenyltriethoxysilane, tridecafluorooctyl-1H,2H,2H-octyltriethoxysilane and phenyltrimethoxysilane.
The silsesquioxane polymer may also be a polymeric reaction product that is obtained from copolymerization of the organosilane with a hydride functional silane, preferably trichlorosilane, HSiCl3, or triethoxysilane.
SiO2-rich ceramic thin films may be formed on a substrate by applying a coating composition containing the silsesquioxane polymer of this invention onto a substrate, as described in our U.S. Pat. No. 5,853,808. The coating composition containing the silsesquioxane polymer is preferably a homogeneous liquid that includes an organic solvent for dissolving the silsesquioxane polymer, the solvent being selected from the group consisting of aromatic hydrocarbons and their epoxy-functional derivatives, glycol ethers, alkanes and their epoxy-functional derivatives, ketones, esters and orthoesters, chlorinated hydrocarbons, chlorinated hydrocarbons, chlorofluorocarbons and alcohols.